1. Field of the Invention
The invention relates generally to leather processing and particularly to processes for increasing the usable leather yield from tanned hides.
2. Description of the Prior Art
The recognized need to maximize area yield from a given tanned hide is perhaps virtually as old as the tanning of hides and skins itself. Along with continuing attempts to improve tanning processes are concerted efforts to obtain the highest possible surface area yield. For obvious reasons, unit costs are minimized when a given process produces a greater quantity of useable leather. Accordingly, substantial efforts have been directed throughout the history of leather processing to the attainment of the goal of maximizing leather yield from tanned hides. While stretching, rolling and similar techniques have been tried with mixed success, the non-isotropy of full hides leads to problems with these purely mechanical techniques. In particular, wrinkling of the non-isotropic hides produces substantial barriers to techniques such as simple rolling due to the difficulty in handling of a hide to obtain uniform compression over the full area of the hide and especially in areas of the hide which differ in characteristics, for example, thickness, grain, etc., relative to other and usually major portions of the hides. U.S. Pat. No. 2,884,777 to Kremen details one effort intended to increase the surface area yield of a hide, Kremen describing a two-directional stretching of dressed skins. Kremen particularly describes varying roller structures through which dressed hides are fed in order to stretch the hides and thereby to increase the surface area of the hides. As noted above, difficulties are encountered in the simple rolling of flaccid hides due in part to the difficulty of handling the hides and in part to the non-isotropic nature of the hides as referred to above.
According to the present invention, particular advantages accrue from the freezing of a tanned hide either before or after the splitting process, the splits resulting from the splitting of either a frozen hide or flaccid hide being subjected to mechanical compression while frozen for increasing the surface area yield while actually improving the surface characteristics of the material. In the prior art, Ruedebush, in U.S. Pat. No. 2,374,836, describes the freezing of a tanned hide prior to splitting and shaving and discloses the actual splitting of a frozen hide in order to facilitate processing of the hide. Ruedebush does not, however, provide means for sensing the thickness of a hide and of the splits in order to adjust the position of the hide or cutting element in order to produce uniform splits. Ruedebush also does not disclose additional processing of a frozen split. Trod, in U.S. Pat. No. 2,559,329, also discloses the freezing of a hide in order to facilitate a splitting process.
Cutler, in U.S. Pat. Nos. 2,354,200 and 2,438,150, describes the freezing of tanned hides in order to dry the hides at sub-freezing temperatures. Tsui, in U.S. Pat. No. 4,355,236, and Kline, in U.S. Pat. No. 2,587,405, also describe freezing steps in leather processing although these disclosures do not relate to the subjection of a frozen hide to conditioning by compression or compression of frozen splits in order to increase surface area yield. United Kingdom patent No. 1,103,652, Switzerland patent No. 299,460, and U.S.S.R. patent No. 720,018 also describe the freezing of a hide as a part of a drying operation and particularly vacuum drying operations.
The prior art as noted does not provide for increasing the surface area yield of a tanned hide by freezing of a hide and/or splits from the hide and then subjecting the frozen splits to mechanical compression, such as with biaxial rolling, and with the further advantage of improving the surface characteristics of the resulting leather product.